<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Set 实践</title>
</head>
<body>
    <script>
        let arr = [1,2,3,4,5,4,3,2,1];
        //1. 数组去重
        // let result = [...new Set(arr)];
        // console.log(result);
        //2. 交集
        let arr2 = [4,5,6,5,6];
        // let result = [...new Set(arr)].filter(item => {
        //     let s2 = new Set(arr2);// 4 5 6
        //     if(s2.has(item)){
        //         return true;
        //     }else{
        //         return false;
        //     }
        // });
        // let result = [...new Set(arr)].filter(item => new Set(arr2).has(item));
        // console.log(result);

        //3. 并集
        // let union = [...new Set([...arr, ...arr2])];
        // console.log(union);

        //4. 差集
        let diff = [...new Set(arr)].filter(item => !(new Set(arr2).has(item)));
        console.log(diff);

    </script>
</body>

</html>